package util;

import java.util.function.Consumer;
import java.util.function.Function;

public final class Ref<T> {
	
	private T value;

	private Ref() {

    }

    private Ref(final T value) {
		
		this.value = value;
	}

	public static <T> Ref<T> of(final T value) {

	    return new Ref<>(value);
    }

    public static <T> Ref<T> empty() {

	    return new Ref<>(null);
    }

	public Ref<T> swap(final T value) {
		
		this.value = value;
		
		return this;
	}
	
	public Ref<T> shift(final T value) {
		
		final Ref<T> old = new Ref<>(this.value);
		
		swap(value);
		
		return old;
	}

	public <R> Ref<R> map(final Function<T, R> trans) {

		return isPresent() ? new Ref<R>(trans.apply(value)) : new Ref<>(null);
	}

	public <R> R flatmap(final Function<T, R> trans) {

		return isPresent() ? trans.apply(value) : null;
	}

	public boolean isPresent() {

		return value != null;
	}

	public void ifPresent(final Consumer<T> consumer) {
		
		if(isPresent()) consumer.accept(get());
	}

	public T get() {

		return value;
	}

	public T orElse(final T elseValue) {

		return isPresent() ? get() : elseValue;
	}
}
